1. Field of the Invention
The present invention relates to a camera having a blurring movement correction mechanism, more precisely, it relates to a camera which is equipped with a correction mechanism that detects unintentional movement of hands holding the camera and that cancels the movement of the image formed on the film surface corresponding to the unintentional motion of hands in response to the detection results of the motion of the camera by driving an optical correction unit which is disposed on an optical path of a fixed focal length optical system or a variable focal length optical system of the camera.
2. Description of the Related Art
In general, a camera having an unintentional blurring movement correction or canceling mechanism (which is called simply a camera hereinafter) is constructed in such a way that, in an example where the camera is provided with a zoom lens as a photo-taking optical system, the photo-taking optical system is detachably arranged in the camera as an integral unit of the camera body or through a lens mount and that a film surface is disposed behind the lens system on an optical axis of the lens system.
The photo-taking optical system comprises a focusing lens group constituted from a plurality of lenses and a zooming lens group constituted from a plurality of lenses. A blurring correction optical element is disposed on an optical path of the lens groups.
The focusing lens group is driven to be in an in-focus state by a focus command signal Df. The zoom lens group is driven to achieve a zooming function by a zoom command signal Dz. Also, the blurring correction lens element is driven to correct or compensate for the blur of photo-image caused by unintentional motion of hands by a blur correction command signal Da.
Next, the functional motion of each lens group is described below. The focusing lens group is driven to move forward according as the focal length is shifted to the telescopic side and according as the length to the subject to be taken is shortened.
The zoom lens group is driven to move forward according as the focal length is shifted toward the telescopic side. Similarly, the blur correction optical element is driven to move forward according as the zoom lens group is driven to move toward the telescopic side.
Next, the blur correction command signal Da is more concretely described below.
The example is the case where the oscillation motion of the camera body caused by unintentional movement of hands has an oscillation characteristic of approximately a sine wave form curve (a) representing an amplitude curve that moves to the positive and negative directions from the boundary of zero level.
To correct blur of a photograph, that is, to minimize or compensate for influence to the subject image on the film caused by unintentional movement of hands holding the camera body that blurs the photograph, the blur correction mechanism of the camera is arranged as follows.
First, a hand movement detection unit arranged within the camera body detects the velocity V of the hand movement within a very short period of time. Then, a movement velocity changing amount data B.sub.k is calculated on the basis of the detected velocity data. The blur (hand movement) correction command signal Da is obtained from the velocity changing amount data B.sub.k. The signal Da is used to drive the blur correction optical element to move in the direction in which the motion of the camera caused by the hand movement is canceled so as to prevent the image of the subject on the film surface from moving on the film surface.
The correction motion is always delayed from the actual unintentional motion of the camera.
More precisely, the movement velocity is detected at a plurality of times (t-2It), (t-It), (t), (t+It) . . . , wherein (It) represents the integration time period for each time to detect the velocity. The velocity changing amount data B.sub.k, B.sub.k-1, . . . is calculated on the basis of each velocity detection data. Then, on the basis of each velocity changing amount data B.sub.k, B.sub.k-1, . . . is calculated a camera motion velocity data V.sub.k, V.sub.k-1, . . . which is used to generate the blur correction command signal Da.
Therefore, the image formed on the film surface moves in accordance with a corrected characteristic (f) which is compensated with the use of correction characteristic (d) with respect to the movement amount characteristic (e).
However, in accordance with the above mentioned correction arrangement, only about one fourth of the total movement amount of the camera body can be corrected.
In order to improve this point of correction amount ratio, an arrangement is proposed wherein the input amount to the drive circuit for the blur correction optical element is controlled so as to converge the oscillation of the movement of the camera body at the time of driving the optical system for correcting the movement of the camera.
Such an arrangement is disclosed in Japanese Patent Application Laying Open (KOKAI) No. 1-300221, for instance. In accordance with the arrangement disclosed in the patent document, the amplifying ratio of the drive circuit for the blur correcting optical element is varied in response to the output from the movement detection unit so that the oscillation movement of the camera body caused by the unintentional movement of hands is attenuated to converge.
Also, the above mentioned patent document discloses another arrangement for attenuating the movement of the camera body with the use of the above mentioned electric means for varying the amplifying ratio of the drive circuit wherein the rigidity of the oscillation detecting sensor for detecting the movement of hands holding the camera body is varied to attenuate the oscillation so as to increase the correction amount ratio of the unintentional oscillation.
On the other hand, it is most desirable to use an actuator which is able to function with a very small or almost no time lag as a drive source for driving the blur correcting optical member in a direction for attenuating and converging the blur movement vibration to zero.
However, in the actual arrangement, from the stand point of space for the actuator assembled within the camera body in connection with the power battery means, the blur correction optical member is driven intermittently by a compact stepping motor, a small sized motor or a linear motor type intermittent drive means.
For instance, the actuator is intermittently driven in every minute time of interval (t0) so as to represent an approximation of curve or linear line of the indicated driving wave-form for driving the actuator.
Also, an example of the timing for the intermittent drive of the actuator is such that a 1/2 period of the drive pulse Dp, that is, a time period from a rising point to a subsequent falling point of the pulse is arranged to correspond to one cycle of the driving wave-form to drive the actuator synchronized with the drive pulse signal which has a very short repeating time cycle.
Also, another example of the timing for the intermittent drive of the actuator is such that the 1/2 period of the drive pulse Dp from a rising point to a subsequent falling point is arranged to correspond to one driving cycle of the actuator including one driving wave-form for the actuator and a subsequent short time period represented after the driving wave-form.
Such a curve line of the driving wave-form is processed by sampling detection data at a plurality of timing points so as to obtain a final blurring movement data.
In accordance with the camera of the related art mentioned above, the blurring motion is corrected in such a way that the unintentional motion of hands holding the camera is detected first so that the driving amount for moving the blur correcting optical member is calculated from the detection result and that the optical member is driven on the basis of the calculation result.
However, such an arrangement for driving the blur correcting optical member mentioned above involves in the following problems.
That is, in accordance with the arrangement of the related art mentioned above, a time lag is inevitably generated between the timing points of detecting the blurring movement of hands, calculating the blur correcting data and driving the blur correcting means. Therefore, although it may be possible to correct the blurring movement to a certain extent, the blur is not satisfactorily corrected since a problem of shortage of the correction amount is always involved due to the time lag generated in the blur correcting system.
Such a problem of shortage of the blur correcting amount is not so influential when the absolute amount of the unintentional blurring movement of hands holding the camera is relatively small since the shortage of the blur correcting amount is also small so that the blur can be corrected by the blur correcting system of the related art mentioned above.
However, in the event that the absolute amount of the blurring hand motion becomes large, the shortage of the blur correcting amount becomes large too so that the problem becomes significant.
Also, with regard to the camera of this kind, it is very important to accurately detect the blurring movement of hands holding the camera. For instance, in the case wherein the blurring motion is to be detected with the use of an acceleration sensor type detection means, it is naturally required that the sensitivity of the sensor be high, whereas to the contradiction, if a sensor which is too sensitive is used, the sensor detects minute vibrations generated from the blur correcting optical member at the time of being intermittently operated by the actuator other than the blurring hand motion, as a result of which accuracy of the detection data of the blurring motion is lowered.
This inaccuracy of the detection data is especially significant when the width of the transition noise generated at the time of intermittently driving the blur correcting means is not fully long with respect to the interval of the sampling points of the output data from the blurring motion detection means. That is, the inaccuracy of the detection data is not so influential when the vibration generated from the intermittent drive means is smooth and continuous. However, when the vibration at the time of intermittent drive of the blur correcting means includes a number of impulse components, it becomes difficult to accurately sample the data, which causes to increase the detection error.